This invention generally relates to safety devices for aircraft landing gear and more particularly to a temperature and pressure sensitive valve assembly that prevents tire blowout due to overpressure generated by heat buildup during high energy braking situations.
Fusible plugs have been used for some years in aircraft wheel and tire assemblies as precautionary devices when excessive temperatures are generated in the assembly during high energy braking. The plugs contain a eutectic material that is designed to melt at a temperature below the safe temperature limit of the particular type of tire. When the specific melt temperature is reached, the fusible plug softens and/or melts to the extent that it is blown out by reason of increased tire pressure thus venting the tire and preventing tire blowout and/or explosion.
Devices of this type are taught and illustrated in the following prior art patents: U.S. Pat. No. Re. 26,137 (G. E. Stanton); U.S. Pat. No. 2,001,686 (R. H. Moore, et al); U.S. Pat. No. 3,138,406 (R. K. Chamberlain); U.S. Pat. No. 3,269,402 (R. F. Horner); U.S. Pat. No. 3,517,683 (H. R. Chandler); U.S. Pat. No. 3,559,668 (R. L. Crossman); U.S. Pat. No. 3,991,804 (M. E. Wilson); U.S. Pat. No. 4,365,643 (Masclet, et al); and British No. 782,559 (Bendix Corp.).
While these prior art devices work in their intended applications, they are not practical for use on modern aircraft which travel at greater speeds and carry increasingly heavier loads. The reason for this is the fact that all of these prior art devices are intended to blow the fuse plug at a particular temperature limit whereupon complete deflation of the associated tire results. In this circumstance, a deflated tire operating at high speed will result in heat buildup in the tire carcass and ultimate total destruction by explosion of the tire. Furthermore, it has been shown that when one tire of a pair on a landing gear strut is deflated, the opposite tire bears the increased load which may result in its destruction also. In any event and in a situation of an aircraft operating at high speed with a deflated tire, the result is extremely hazardous and may be catastrophic to the aircraft. Therefore, the fusible plugs of the prior art, while saving the particular tire experiencing overpressure due to heat buildup, are not the ultimate answer to the tire deflation problem and the hazard which such creates for a high speed and heavily loaded aircraft.
Accordingly, the present invention provides a solution to the problem by providing a fusible plug and valve assembly that protects a tire from overpressure by venting off the overpressure at a particular temperature limit but also maintains a minimum safe tire pressure. This allows the tire to continue to be operational and bear its share of the load until the aircraft is safely stopped.